54 ANIMAL CHEMISTRY LECTURE III. 



Nitrous acid Hydrogen Water Ammonia 



HNO a + H 6 2H 2 + H 3 N; 



so that not only is oxygen taken away from, but hydrogen is 

 added to the nitrogen of our original nitrous acid. 



(55.) By combining the oxidised form of nitrogen, or nitrous 

 acid HNO 2 , with the hydrogenetted form of nitrogen, or ammonia 

 H 3 N, we obtain nitrite of ammonia NH 3 HN0 2 , a neutral crystal- 

 lisable salt, whose somewhat concentrated solution is contained in 

 this flask-retort. Now, on applying heat to the retort, observe 

 what takes place. There is, you see, a copious evolution of gas, 

 some of which we will collect over the pneumatic trough ; and, in 

 order to save time, will content ourselves with only a small 

 cylinder full. The gas, produced in this manner from the nitrite 

 of ammonia solution in the retort, is nitrogen, recognisable at 

 once by its property of extinguishing flame. In this decomposi- 

 tion then the hydrogen of the ammonia exactly suffices to remove 

 the excess of oxygen from the nitrous acid, whereby the nitrogen 

 of both constituents of the salt is simultaneously liberated, 

 thus:- 



Ammonia nitrite Water Nitrogen 



NH 3 HNO Z = zH a O + N, 



Hence nitrogen may be looked upon as exactly intermediate in 

 its state of oxidation between nitrous acid on the one hand, and 

 ammonia on the other ; whilst ammonia must be considered the 

 extreme product of deoxidation. Accordingly, it lias been found 

 as a general result both of laboratory and field experiments, the 

 latter conducted more especially by Messrs. Lawes and 'Gilbert in 

 this country, that cereals and other plants thrive equally well 

 upon salts of nitrous or nitric acid as upon salts of ammonia ; 

 and that when a plant is supplied with water, carbonic acid, and 

 nitrous acid, it exerts upon the nitrous acid the same sort of re- 

 ducing action that it does upon the water and carbonic acid, 

 whereby not only amylaceous, but ammoniated or nitrogenised 

 principles are abundantly produced. Indeed some chemists have 

 maintained that nitrous acid, rather than ammonia, forms the 



